linux-kernel - Re: [syzbot] [fs?] WARNING in free_mnt

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Message-ID: <20251001004317.7786-1-hdanton@sina.com>
Date: Wed,  1 Oct 2025 08:43:11 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+7d23dc5cd4fa132fb9f3@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [fs?] WARNING in free_mnt_ns

> Date: Tue, 30 Sep 2025 13:17:34 -0700	[thread overview]
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    449c2b302c8e Merge tag 'vfs-6.18-rc1.async' of git://git.k..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15b43858580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=595e5938a1dd5b4e
> dashboard link: https://syzkaller.appspot.com/bug?extid=7d23dc5cd4fa132fb9f3
> compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11c9ad04580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=160bf27c580000

#syz test

--- l/fs/namespace.c
+++ n/fs/namespace.c
@@ -4092,8 +4092,12 @@ static void dec_mnt_namespaces(struct uc
 
 static void free_mnt_ns(struct mnt_namespace *ns)
 {
-	if (!is_anon_ns(ns))
-		ns_common_free(ns);
+	if (!is_anon_ns(ns)) {
+		struct ns_common *nsc = to_ns_common(ns);
+
+		if (nsc->inum != MNT_NS_ANON_INO)
+			ns_common_free(ns);
+	}
 	dec_mnt_namespaces(ns->ucounts);
 	mnt_ns_tree_remove(ns);
 }
--